Misaka Imouto image - RK44

Introduced in both the third volume of the novel and manga respectively, and episode ten of the anime, Touma meets the younger 'twin sister' of Misaka Mikoto who he calls Misaka's sister (御坂妹, Misaka imouto?) who seems rather quiet and emotionless. Her voice is rather monotone and machine like and her speech pattern is unique as she speaks, she adds a description of herself speaking before in third person. Despite this, she has a soft spot for cats. Mikoto seems to dislike and worry about her for some reason and later events reveal why.

In reality, Misaka Imouto is a clone of Mikoto, in fact she is No. 10032 out of 20000 other clones copied from Mikoto called 'The Sisters'.

Even though they have a weaker variant of Mikoto's powers of electricity, all of their minds are connected together using a special psychic ability called Radio Noise (欠陥電気, Kekkan Denki?, "Flawed Electric"), an ability which lets their brainwaves become electric signals, which allows them to share memories thanks to their communication network, a.k.a. the Misaka Network, it uses the Radio Noise to a great extent and works like the Internet, sharing information with each other. Being rapidly manufactured clones, they do not change their facial expression much, as they did not learn how to.

Even though 20,000 clones were created in total, all clones below No. 10032 were killed earlier and are being used in an experiment designed to create the first Level 6 psychic ("Level 6 Shift").